Vehicle evaporative emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of undesired evaporative emissions that could release fuel vapors to the atmosphere.
Undesired evaporative emissions may be identified using engine-off natural vacuum (EONV) during conditions when a vehicle engine is not operating. In particular, a fuel system and evaporative emissions control system may be isolated at an engine-off event. The pressure in such a fuel system and evaporative emissions control system will increase if the tank is heated further (e.g., from hot exhaust or a hot parking surface) as liquid fuel vaporizes. If the pressure rise meets or exceeds a predetermined threshold, it may be indicated that the fuel system and the evaporative emissions control system are free from undesired evaporative emissions. Alternatively, if during the pressure rise portion of the test the pressure curve reaches a zero-slope prior to reaching the threshold, as fuel in the fuel tank cools, a vacuum is generated in the fuel system and evaporative emissions system as fuel vapors condense to liquid fuel. Vacuum generation is monitored and undesired emissions identified based on expected vacuum development or expected rates of vacuum development. The EONV test may be monitored for a period of time based on available battery charge.
However, the EONV test is prone to false failures based on customer driving and parking habits. For example, a refueling event that fills the fuel tank with relatively cool liquid fuel followed by a short ensuing trip may fail to heat the fuel bulk mass and may result in a false fail if an EONV test is run. Further, the rates of pressure build and vacuum development are based in part on the ambient temperature. During mild weather conditions, the ambient temperature may restrict the amount of heating or cooling of the fuel tank following engine shut-off, and thus limit the rate of pressure or vacuum development. As such, in a case wherein a pressure build does not reach the expected threshold, the subsequent vacuum build may additionally not reach expected threshold level in the time allotted for the EONV test based on available battery charge. This may result in a false-fail condition, leading to potentially unnecessary engine service.
US Patent Application US 20140074385 teaches during engine-off conditions, operating a fuel pump coupled to the fuel tank to initiate an evaporative emissions test. By operating the fuel pump, fuel in the fuel tank is agitated, causing a fuel vapor pressure to increase. Following the fuel tank pressure build-up, pump operation is discontinued, and a rate of pressure decay or bleed-down is monitored and compared to a threshold rate. However, the inventors have recognized a potential issue with such a method. For example, the method cannot be used to supplement a pressure rise during the course of an EONV test, due to confounding noise factors associated with the agitation of fuel by the fuel pump.
U.S. Pat. No. 9,140,627 teaches during a vacuum portion of an EONV test, operating a cooling fan to increase a fuel system vacuum, and indicating the presence or absence of undesired evaporative emissions based on the increased vacuum. However, the inventors have recognized a potential issue with such a method. For example, while the method may serve to facilitate an increased level of vacuum during the vacuum build portion of an EONV test, the portion of the EONV test wherein a pressure build is monitored is not able to be manipulated by such a method.
The inventors herein have recognized the above issues, and developed systems and methods to at least partially address the problems. In one example a method is provided, comprising during an engine-off condition and responsive to predetermined test conditions, sealing the fuel tank and the emission system from atmosphere, and routing engine heat through a passenger cabin of the vehicle to the fuel tank.
As one example, routing engine heat through a passenger cabin of the vehicle to the fuel tank comprises a pressure increase in the fuel tank and emission system below an expected threshold pressure level while the fuel tank and emission system are sealed, wherein the pressure increase is monitored, or inferred. In this way, responsive to an indication that a pressure increase in the fuel tank and emission system is below an expected threshold pressure level while the fuel tank and emission system are sealed, engine heat may be routed through the passenger cabin of the vehicle to the fuel tank, thereby increasing pressure in the fuel tank and emission system. By actively increasing pressure in the fuel tank and emission system, pressure in the fuel tank and emission system may reach the expected threshold pressure level, thus indicating an absence of undesired evaporative emissions under circumstances where undesired emissions are not present. By enabling the option to actively pressurize the fuel tank and emission system, reliance of the EONV test on environmental factors and vehicle operator driving habits may be reduced, thus increasing completion rates and reducing false-failures during evaporative emissions diagnostic tests.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.